A system for measuring air pressure of vehicle tires and informing a driver of information regarding the measured air pressure and beforehand preventing the risk of an accident by providing warning signals to a driver when the air pressure of the tires is below specified pressure is referred to as a tire pressure monitoring system (hereinafter, referred to as TPMS).
TPMSes utilize either an indirect scheme and a direct scheme. The indirect scheme senses RPM of each wheel by an anti-lock brake system (ABS) sensor to sense a state of tires and the direct scheme senses the pressure of tires by embedding the air pressure sensors in the tires.
The indirect scheme has degraded reliability. As a result, the TPMS using the direct scheme has been commercialized.
TPMSes using the direct scheme include a “high-line” type and a “low-line” type.
The low-line type can warn only when tires are not within the specified pressure range, while the high-line type can indicate which positions of the tires are not within the specified pressure range by adding four low frequency initiators (LFIs) around each tire.
A high-line TPMS includes four separate LFI—one for each TPMS sensor in the vicinity of each tire so as to detect the positions of the sensors. Therefore, cost and weight of the TPMS are increased and assembly time can be increased.